In a X-ray flat panel detector (FPD) to be employed in a clinical site, X-rays transmitted through a subject are received by scintillators and lights emitted from the scintillators are detected by photodetectors. The photodetectors are arranged in two-dimensional array and the scintillators are separated by voids so as not to give rise to any crosstalk of light. Light emitted from the inside of the scintillators is repeatedly reflected at the boundaries of the voids to suppress scattering of light in directions on a plane perpendicular to the travelling direction of light. As a result, a highly sharp radiation image can be obtained (see, PTLs 1 through 3).
For example, PTL 1 discloses a method of applying slurry which is prepared by dispersing a fluorescent material in water to a substrate, causing the slurry to freeze to form ice pillars in the slurry, subsequently removing the ice pillars and calcining the resultant substrate to produce voids in the slurry of the fluorescent material.